Rock-blasting cartridge and blasting method

ABSTRACT

A blasting cartridge comprising an elongated sleeve extending along an axis A and having a first end and a second end; the first end has a first sleeve closure with an opening for holding a detonator; the second end has a second sleeve closure; a space is provided between the first sleeve closure and the second sleeve closure for holding a blasting explosive; wherein the second end is provided with a connector means for releasably connecting the second end of the cartridge with a first end of an adjacent cartridge and comprising a firing pin means for impinging upon a detonator in the first end of the adjacent cartridge when the blasting explosive is detonated by actuation of the detonator in the first end of the cartridge.

This invention relates to blasting cartridges used in rock breakingmethods such as disclosed, for example, in U.S. Pat. No. 4,382,410 or EP248 610. In such methods, a hole is drilled into the rock and afterinserting one or more blasting charges the hole is filled with water,and a so-called rock breaking tool is inserted into the hole. If therock is porous a gel-forming agent may be added to the water. The toolcan be operated to detonate the blasting charge, generally by igniting aprimary or starter charge arranged within the tool and generating ashock wave which is propagated by the water and ignites the cartridgesthat constitute the actual or secondary charge within the water-filledhole.

Various and widely differing types of cartridges for the secondarycharge are known. More recent cartridge types are disclosed in U.S. Pat.No. 6,516,725 where each cartridge is provided with a detonator (alsotermed percussion cap) and a firing pin body, or in WO 2005-088236 wherethe cartridges are provided with protrusions at one of their ends toassure that the igniting shock produced in the water by the primarycharge has free access to the ignition-sensitive portion of thesecondary blasting cartridge or cartridges.

Yet, none of the known types of cartridges guarantees safe ignition ifseveral cartridges are arranged one behind the other in the bore holeand it is a main object of the invention to provide for a blastingcartridge where failure to ignite the cartridge most remote from theprimary charge virtually is excluded even if a large number ofcartridges is required for a given operation. Another object of theinvention is the capacity to form coherent elongated bodies of severalcartridges to facilitate handling, e.g. when charging the hole drilledinto the rock or when the need arises to withdraw a charge withoutignition.

Now, in order to meet theses objectives the present invention, in afirst aspect thereof, provides for a blasting cartridge as defined inclaim 1. Preferred embodiments of the blasting cap according to theinvention are as defined in claims 2-8.

According to a second aspect the invention provides for a blastingmethod wherein a blasting explosive is positioned within an tubular holedrilled into a rock and initiated by a primary charge for actuation of aplurality, e.g. 2-8, of interconnected blasting cartridges according tothe invention. Preferably, the cartridges fit snugly into the holedrilled into the rock, typically with a gap of only a few millimetres.As is conventional, the inter-space between the cartridges and the rockis filled With an aqueous medium which may contain a thickener orgel-former if the rock is porous.

Generally, the blasting cartridge according to the invention has anelongated and preferably tubular or cylindrical sleeve; reference to theaxis serves for purposes of clear definition and relates to thegeometric axis along the longest extension of the cartridge. extendingalong an axis (A) and having

The cartridge has a first or “upper” end and a second or “lower” end.and each end is provided with a closure. The terms “upper” and “lower”are subjective, of course, but serve to illustrate the gist of theinvention since the cartridges are intended for use in rock blastingwhere a hole is drilled into the rock and the charge is inserted so thateach lower end of a cartridge is more remote from the opening of thehole than the upper end of the same cartridge.

Each first end of a cartridge holds a detonator or percussion cap suchas used with the cartridges which is sensitive to the shock of a firingpin. Centre-fire detonators are preferred over rim-fire detonatorsherein. The closure of the cartridge adjacent the upper end is aradially extending wall with a central opening that receives and holdsthe detonator.

Each second end of a cartridge is provided with a connector means forreleasably connecting the second or lower end of the cartridge with afirst end or upper end of an adjacent cartridge and comprises a firingpin means for impinging upon a detonator in the first end of an adjacentcartridge.

The space between said first sleeve closure and said second sleeveclosure of the cartridge contains a conventional blasting explosive,preferably one having an energy of 4000-5000 Joule/g. Actuation of thedetonator means triggers the ignition of the blasting explosive.

Typically, blasting cartridges according to the invention are used inthe manner disclosed in WO2005/088236 mentioned above, i.e. as a“cracker” or “secondary” charge which typically is ignited by a smallercartridge termed “starter” of the conventional shotgun type as shown,for example, in U.S. Pat. No. 670,737 mentioned above. Suitable startercartridges are well known in the art and are available commercially sothat a more detailed explanation of their structure and associatedfiring apparatus are not discussed herein.

While the connector according to the invention could be an integral partof the cartridge, or cartridge sleeve, respectively, it is mostpreferably used in the form of a separate integral or “monolithic”structure made of a synthetic polymer, typically a thermoplastic polymersuch as a polyamide, polyalkylene, polystyrene, ABS-resin, polyurethane,or the like material containing the usual fillers, additives,stabilizers, pigments, etc., shaped e.g. by injection moulding or othershaping methods. The sleeve can be made of the same material as theconnector or a differing material of the type conventionally used forblasting cartridges.

A preferred embodiment will be explained in more detail below and withreference to the drawing in which:

FIG. 1A is a cross-sectional semi-diagrammatic view of the sleeve of acartridge in upside-down position prior prior to its assembly with thedetonator and blasting explosive and with the connector shown separatelyon top;

FIG. 1 B is a cross-sectional view of the cartridge components in afully assembled state; and

FIG. 2 is a semi-diagrammatic view of two adjacent cartridges in theirinter-connected state.

The blasting cartridge 10 depicted in FIG. 1A comprises an elongatedcylindrical sleeve 12 that extends along its longitudinal axis A and hasan outer diameter D_(o) and an inner dimeter D_(i). Typically, Do is inthe range of from about 20-50 mm, e.g. 35 mm. The thickness of sleevewall 120 typically is in the range of from about 1-5 mm resulting in aninner diameter in the range of from about 22-48 mm.

Due to the upside-down showing of FIG. 1A, the connector 14 is shownnear the second or lower end 122 prior to insertion of connector 14 intosleeve 12 so as to eventually form the “lower” end of space 17 prior tofilling that space with blasting explosive, typically a granulate.Finally, detonator or (a “percussion cap”) 15 is inserted into thecircular opening at the centre of radially extending wall 124 which isoffset in axial direction so as to form a collar 126 around detonator25.

Connector 14 has a flange portion 144 with the same diameter as sleeve12 so as to limit motion of a generally tubular end 142 of connector 14when pressed into sleeve 12. Dimensions and shape of end 142 areselected to ascertain a tight fit in the lower end 122 of sleeve 12 sothat it will not be separated easily—and may even be glued or welded ifrequired—and in any case will maintain its connection with sleeve 12even when two cartridges are connected (as indicated in FIG. 2) andseparated again, e.g. if an assembled blasting charge consisting of twoor more connected cartridges is to be disassembled.

It will be appreciated that while a monolithic connector is preferredfor various reasons, the invention includes a cartridge where theconnector 14 is an integral part of the sleeve or a sleeve portion.

Bulge 140 of connector 14 serves as a “firing pin” means where the word“pin” is used herein merely as a functional term and not to define ashape. In fact, what is meant herein by the term “firing pin” is afiring actuator, i.e. the part which impinges on the detonator of anadjacent cartridge (FIG. 2). Preferably, the annular portion 148 aroundbulge 140 is the thinnest part of the outer wall of the final cartridge(FIG. 1B) so that separation of the firing pin means will occur mosteasily upon blasting. Connector 14 is provided with a second tubularprotrusion 146 for connection with an adjacent cartridge as will beexplained in connection with FIG. 2. Generally, portion 148 will be atleast about 10% thinner than any other portion of the outer wall ofcartridge 10, preferably at least 20%.

FIG. 1 B shows a fully assembled blasting cartridge according to theinvention. Typically, a detonator is inserted into opening 125 so as toclose the associated end of sleeve 14. Blasting explosive 170, typicallya commercially available granular or pulverulent material, is pouredinto space 17 and connector 14 is inserted into sleeve 17, e.g. bypressing to arrive at the structure of cartridge 10 depicted in FIG. 1A.

FIG. 2 is a semi-diagrammatic sectional view showing a first cartridge20 a (with its central portion broken away and without showing theblasting charge) connected with a second cartridge 20 b (only upperportion shown in FIG. 2). As is apparent from FIG. 2, collar 226 b(which corresponds with collar 126 of FIG. 1A) cooperates with theprotruding portion 246 (corresponding with 146 in FIG. 1A) to hold bothcartridges 20 a,20 b connected while maintaining a predetermineddistance between the end of firing pin 249 and detonator 25 b of theadjacent cartridge 20 b. Collar 246 will also serve to protect firingpin 240 from damage upon storage or handling while collar 226 (or 126 inFIG. 1A) serve to protect the detonator 15, 25 a,25 b.

As will be apparent from FIG. 2, the gap between firing pin anddetonator can be determined by either or both the axial length of collar14,24 and the axial length of protrusion 146 or 246.

Various modifications will be apparent to those experienced in the artof rock blasting. For example, while drill holes in the suitable forfilling with water, i.e. “downward-directed”, are preferred; upwardsdirected holes in rock could be used and filled with a fluid compositioncapable of become solid within a short time, e.g. because of catalystactuion. Also whenever the term “about” or an equivalent indefinite termis used herein, this indicates a possible variation by ±30%.

1. A blasting cartridge comprising: an elongated sleeve extending alongan axis A and having a first end and a second end, said first end havinga first sleeve closure and an opening for holding a detonator and saidsecond end having a second sleeve closure; and a space between saidfirst sleeve closure and said second sleeve closure for holding ablasting explosive; wherein said second end is provided with a connectormeans for releasably connecting said second end of said cartridge with afirst end of an adjacent cartridge and comprising a firing pin means forimpinging upon a detonator in said first end of said adjacent cartridgewhen said blasting explosive is detonated by actuation of said detonatorin said first end of said cartridge.
 2. The blasting cartridge asclaimed in claim 1 wherein said elongated sleeve has an essentiallycylindrical shape with an outer diameter Do and an inner diameter Di;and wherein said connector means is formed as a separate monolithicmember comprising: a flange having the same radial diameter D as saidsleeve; a first connecting member extending essentially in a first axialdirection from said flange and being shaped for tightly inter-fittingwith said second end of said sleeve; a second connecting memberextending essentially in a second axial direction opposite said firstaxial direction from said flange and being shaped for tightlyinter-fitting with a first end of an adjacent blasting cartridge; and afiring pin means for actuating a detonator in a first end of an adjacentcartridge.
 3. The blasting cartridge of claim 2 wherein said sleeve atsaid first end forms a collar for receiving and tightly holding saidsecond connecting member while maintaining a predetermined gap betweensaid firing pin means and an adjacent detonator.
 4. The blastingcartridge of claim 2 wherein said firing pin means is a protrusionsurrounded by an annular region which is thinner by at least about 10%than any wall material of said cartridge.
 5. The blasting cartridgeaccording to claim 1, wherein said detonator is a center-sensitivedetonator.
 6. The blasting cartridge according to claim 2, wherein saidconnector means is formed of a synthetic polymer.
 7. (canceled) 8.(canceled)
 9. The blasting cartridge of claim 3 wherein said firing pinmeans is a protrusion surrounded by an annular region which is thinnerby at least about 10% than any wall material of said cartridge.
 10. Theblasting cartridge according to claim 2, wherein said detonator is acenter-sensitive detonator.
 11. The blasting cartridge according toclaim 3, wherein said detonator is a center-sensitive detonator.
 12. Theblasting cartridge according to claim 4, wherein said detonator is acenter-sensitive detonator.
 13. The blasting cartridge according toclaim 3, wherein said connector means is formed of a synthetic polymer.14. The blasting cartridge according to claim 4, wherein said connectormeans is formed of a synthetic polymer.
 15. The blasting cartridgeaccording to claim 5, wherein said connector means is formed of asynthetic polymer.
 16. A blasting method comprising the steps of:forming a rod-like charge comprised of a plurality of blastingcartridges mutually connected by a link formed of a connector meansbetween any two adjacent cartridges; positioning the rod-link chargewithin a tubular hole drilled into a rock; and initiating a primarycharge for actuation of the plurality of blasting cartridges.
 17. Theblasting method of claim 10, wherein the tubular hole has an innerdiameter not exceeding twice the outer diameter of the blastingcartridge.